It’s nice and easy to upgrade your environment with a SkyBox. Generate a nice 6 sided cubemap. Use a simple centered Box as Geometry. Translate the box to camera position. Apply the ViewProjection. Set pos.z = pos.w to fit allways to farplane. Use the ModelVertexPosition to sample the cubemap.
That’s it…

Some Problems to fix
• you have to change the cullmode, because you are in the box
• you have to set the DepthComparison to LessEqual, because it’s equal

Some Improvements
• draw the box allways as last opaque object
• adjust the Y position
• use a wider field of view for the box
• draw a sun spot for directional light
• draw the sun spot to glow target for BloomEffect
• the sun spot only works if you use averaged model normals